Introduction: Building a Small Cable Suspension Bridge - the Basics Plus a Video Demo
We built this bridge and wrote a “how we did it” book about the process a few years ago. I thought it would be fun to share the basics of this design as an Instructable for people who have enough skill to be able to take the information and work with it. And as we do in our book, we recommend having your specific design approved by an engineer just to be on the safe side.
So here you go! We also have a blog with a fairly recent materials price list, hints and tips, and other projects. Link is at the end of this Instructable.
Step 1: The Design
Here is our design for an 80’ long walking bridge that spans our creek and is set back far enough for a serious flood. The challenge was to do as much as possible without the need of machinery or swimming. Even if your creek isn’t that wide, consider flood stage and go from there.
The drawing shows everything used to build the bridge other than the cable locking system, which is pictured below and in the video.
Step 2: Install Four Posts
After clearing a site, we installed four posts.
Step 3: The Dead Men...
Dead men are a vital part of this design (the foundation in the ground). Engineered based on the load, they were were buried and secured before the suspension cables were brought in.
Step 4: Build the Cable System
The suspension cables and stringers were cut and assembled off-site. Because of the Golden Gate style, the stringers each had to be a specific height to keep the deck level, actually, slightly crowned.
Step 5: Consider Resonance
The stringers were also spaced to deal with harmonic resonance. Though keep in mind, it’s a suspension bridge and it will move when you walk on it. Whee!
Step 6: Span the Cables and Stringers
Use of a truck on one side of the creek transported the cables across the creek with the stringers rolled up so they didn't tangle. The cables were secured into place.
Step 7: Add the Support Beams
We used our patented Cable Locking System to attach the beams. This system allows for assembly “on the fly” and easy repair/replacement of the beams (joists) if needed. Temporary planks were set out as we worked our way across the span.
The movie shows exactly how the cable locking system works. The magic of the system is the reversed keyhole arrangements between the two components.To note, the email and website given at the end are no more. YouTube doesn't let us edit videos.
Step 8: Add the Decking
Once the beams were in place, we added decking.
Step 9: Now We Can Get to the Other Side and Stay Dry!
This bridge has been our access across the creek to get to our spring for many years, and is holding up great through several major floods. A couple of trees have hit it, but it wasn’t phased. We recently adjusted the turnbuckles on the dead men cables to pull up the slack in the deck from tree hits.
Step 10: For More Information...
Note that all photos and illustrations are from our book, Building a Small Cable Suspension Bridge with the Cable Locking System. The book is easily found on Amazon.com if you look it up, and our blog with more info is wildcatman.wordpress.com. Hopefully this is enough information to get you inspired!